General paralysis of the insane (GPI) was one of the most devastating diseases observed in British psychiatry during the century after 1840, in terms of the high number and type of patients diagnosed, the severity of its symptoms and, above all, its utterly hopeless prognosis. With particular reference to the physicians and patients of the Royal Edinburgh Asylum, this article explores the diagnostic process and the social and medical significance of the 'death sentence' that accompanied the GPI diagnosis.